Camera button rebinding and lockscreen action additions (1/2)

Adds new config_deviceHardwareKeys bitmask for camera button.
Lets you rebind the camera press/longpress and adds a new KEYCODE_CAMERA handler to inject a longpress KeyEvent
in order to let you bind keys to actually trigger the shutter, in addition to launching the app itself.

This also adds KEYCODE_ASSIST and KEYCODE_APP_SWITCH to the available keys to assign longpress lockscreen actions to.

Change-Id: I63583dbbaa0f6a3d21724f4948f86bb01e44b71b